Javascript callback function with parameter?

Question

I have this simple code :

console.log('calling doWork func...')
doWork('a', 'b', myCb);

function doWork(param1, param2, callback)
{
        console.log('in func')
        callback();
}


function myCb(a)
{
        console.log('in callback... for value ' + a)
}

I'm running the function with a callback function -

The output I get is :

"calling doWork func..."
"in func"
"in callback... for value undefined"    // notice the undefined

All ok.

Now, I want the callback to be called with a specified param - something like ( which is incorrect since the () is executing the func) :

doWork('a', 'b', myCb('xxxx'));

I want the output to be :

in callback... for value  xxxx

How do I send a parameter with the myCb call in doWork('a', 'b', myCb);? ( 'when you run the callback function , please run it according to value xxxx')

any help ?

p.s. I want to avoid any global flags solution

thanks.

may be duplicated http://stackoverflow.com/questions/1997531/javascript-callback-function-and-parameters — mask8, Jul 25 '12 at 07:01
@mask8 please search the term `.bind` in your link , I *don't* see it. so I assume it is not duplicate ( different solutions) — Royi Namir, Jul 25 '12 at 07:02
how about this one? http://stackoverflow.com/questions/3458553/javascript-passing-parameters-to-a-callback-function there are too much of this questions anyway — mask8, Jul 25 '12 at 07:07
@RoyiNamir when that first question was written, ES5 had been approved [less than a month prior](http://www.ecma-international.org/news/PressReleases/PR_Ecma%20approves%20major%20revision%20of%20ECMAScript.htm). At that time, most browsers didn't support it, and most developers weren't familiar with it. The lack of `.bind` in the answers is definitely not suggestive that it is not a duplicate (and *certainly* not conclusive in any case). — apsillers, Jul 25 '12 at 07:10

katspaugh · Accepted Answer · 2012-07-25T07:12:11.350

4

The common solution is to create another function in place.

doWork('a', 'b', function () {
    myCb('xxxx');
});

You can also use a function that would abstract the currying away. JavaScript (ES5) even has one built-in – Function.prototype.bind. Mind you, the native bind will make your callback slow and has limited support in browsers (see the MDN page).

doWork('a', 'b', myCb.bind(null, 'xxxx'));

edited Jul 25 '12 at 07:12

answered Jul 25 '12 at 06:58

katspaugh

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What are the issue(s) with the native bind? – Jul 25 '12 at 07:04
1

@pst, while binding a context, it also allows `call` and `apply` to redefine it dynamically. Try to implement such `bind`, and you'll see. That makes each call to a bound function slow. [jsperf](http://jsperf.com/artificial-vs-native-bind/3) – katspaugh Jul 25 '12 at 07:07

score 1 · Answer 2 · answered Jul 25 '12 at 07:00

1

One of the solutions is to use .bind:

doWork('a', 'b', myCb.bind(null, 'xxx'));

answered Jul 25 '12 at 07:00

freakish

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score 1 · Answer 3 · answered Jul 25 '12 at 07:07

1

Or you could use apply and arguments

console.log('calling doWork func...')
doWork('va', 'b', myCb);

function doWork(param1, param2, callback)
{
        console.log('in func')


        callback.apply(this,arguments);
}


function myCb(a)
{
        console.log('in callback... for value ' + a)
}

JSbin Example

answered Jul 25 '12 at 07:07

Moritz Roessler

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oh i see, i mistook the a, from cb with the first argument, you want to pass to the cb function then this won't help you – Moritz Roessler Jul 25 '12 at 07:14

sasikals26 · Answer 4 · 2012-07-25T07:12:15.793

0

console.log('calling doWork func...')
doWork (myCb, "a", "b");
function doWork (callback) {
console.log('in func')
callback (arguments[1], arguments[2]);
}
function myCb (param1, param2) {
console.log('in callback... for value ' + param1)
}

Hope this help you

edited Jul 25 '12 at 07:12

answered Jul 25 '12 at 07:02

sasikals26

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Javascript callback function with parameter?

4 Answers4